Effective Oil and Gas well control is an important element of safety in the hydrocarbons industry. In recent times, subsurface shut in valves have become common additional well control devices.
Subsurface shut in valves are located some distance below the wellhead, and are designed to close (or be closed) in the event of an emergency, thus shutting the well in and preventing further flow of hydrocarbons. They are located at a sufficient depth that accidental damage or deliberate sabotage to the wellhead will leave the subsurface shut in valve intact, and able to stop the dangerous uncontrolled flow of hydrocarbons to the surface. In addition to being an extreme hazard, uncontrolled flow of hydrocarbons causes significant environmental damage and economic loss.
Subsurface shut in valves are designed to “fail safe”, meaning that they are naturally biased (using springs or hydraulic accumulators) to close. They are usually hydraulically actuated, held in the open position by an actuator supplied with pressurised fluid down a tube (“line”) from the surface. This line runs up to a pressure control panel on the surface, and a manual emergency shut in valve, that when activated, releases the hydraulic pressure and so shuts in the well.
For safety reasons, the manual hydraulic shut in valve (and the pressure control panel) is often located some distance from the well, so that if the well is on fire then the manual emergency shut in valve can still be activated. For the same reason, the manual emergency shut in valve is generally located in a direction that is upwind in the prevailing wind.